linux-kernel - Re: [PATCH v6 05/14] rust: hrtimer: allow timer restart from timer handler

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Message-ID: <CAJ-ks9=0HRjwqqrLZ2QjyjYw6frK=zu5_ZG5Jmb=fCRXefBmLQ@mail.gmail.com>
Date: Tue, 14 Jan 2025 12:32:45 -0500
From: Tamir Duberstein <tamird@...il.com>
To: Andreas Hindborg <a.hindborg@...nel.org>
Cc: Miguel Ojeda <ojeda@...nel.org>, Anna-Maria Behnsen <anna-maria@...utronix.de>, 
	Frederic Weisbecker <frederic@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, 
	Danilo Krummrich <dakr@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Alice Ryhl <aliceryhl@...gle.com>, 
	Trevor Gross <tmgross@...ch.edu>, Lyude Paul <lyude@...hat.com>, Guangbo Cui <2407018371@...com>, 
	Dirk Behme <dirk.behme@...il.com>, Daniel Almeida <daniel.almeida@...labora.com>, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 05/14] rust: hrtimer: allow timer restart from timer handler

On Fri, Jan 10, 2025 at 3:17 PM Andreas Hindborg <a.hindborg@...nel.org> wrote:
>
> This patch allows timer handlers to report that they want a timer to be
> restarted after the timer handler has finished executing.
>
> Also update the `hrtimer` documentation to showcase the new feature.
>
> Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
> ---
>  rust/kernel/time/hrtimer.rs     | 37 ++++++++++++++++++++++++++++++++++++-
>  rust/kernel/time/hrtimer/arc.rs |  4 +---
>  2 files changed, 37 insertions(+), 4 deletions(-)
>
> diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
> index d0842c7c4c6ddffeef9a79cbf9727819060e4333..50e8c23578b5cf7196893ac88d9547fc027f1f04 100644
> --- a/rust/kernel/time/hrtimer.rs
> +++ b/rust/kernel/time/hrtimer.rs
> @@ -167,7 +167,7 @@ pub trait HrTimerCallback {
>      type CallbackTargetParameter<'a>;
>
>      /// Called by the timer logic when the timer fires.
> -    fn run(this: Self::CallbackTargetParameter<'_>)
> +    fn run(this: Self::CallbackTargetParameter<'_>) -> HrTimerRestart
>      where
>          Self: Sized;
>  }
> @@ -262,6 +262,41 @@ unsafe fn start(self_ptr: *const Self, expires: Ktime) {
>      }
>  }
>
> +/// Restart policy for timers.
> +pub enum HrTimerRestart {
> +    /// Timer should not be restarted.
> +    NoRestart,
> +    /// Timer should be restarted.
> +    Restart,
> +}
> +
> +impl From<u32> for HrTimerRestart {
> +    fn from(value: u32) -> Self {
> +        match value {
> +            0 => Self::NoRestart,
> +            _ => Self::Restart,
> +        }
> +    }
> +}
> +
> +impl From<i32> for HrTimerRestart {
> +    fn from(value: i32) -> Self {
> +        match value {
> +            0 => Self::NoRestart,
> +            _ => Self::Restart,
> +        }
> +    }
> +}

These are for converting from bindings to our enum, right? Why do we
need both signed and unsigned, and why do we hardcode 0 rather than
using the generated constants?

> +
> +impl From<HrTimerRestart> for bindings::hrtimer_restart {
> +    fn from(value: HrTimerRestart) -> Self {
> +        match value {
> +            HrTimerRestart::NoRestart => bindings::hrtimer_restart_HRTIMER_NORESTART,
> +            HrTimerRestart::Restart => bindings::hrtimer_restart_HRTIMER_RESTART,
> +        }
> +    }
> +}
> +
>  /// Use to implement the [`HasHrTimer<T>`] trait.
>  ///
>  /// See [`module`] documentation for an example.
> diff --git a/rust/kernel/time/hrtimer/arc.rs b/rust/kernel/time/hrtimer/arc.rs
> index 4c1812f190bc7a9e0b2fcd5ea2e320f45ba584bc..cee143b04aa21fa6c60c3363cd95f7a67360cbf8 100644
> --- a/rust/kernel/time/hrtimer/arc.rs
> +++ b/rust/kernel/time/hrtimer/arc.rs
> @@ -82,8 +82,6 @@ impl<U> RawHrTimerCallback for Arc<U>
>          // timer. This `U` is contained in an `Arc`.
>          let receiver = unsafe { ArcBorrow::from_raw(data_ptr) };
>
> -        U::run(receiver);
> -
> -        bindings::hrtimer_restart_HRTIMER_NORESTART
> +        U::run(receiver).into()
>      }
>  }
>
> --
> 2.47.0
>
>
>